The first - and in most cases the only - step is to download all your transaction data from OVEX and upload it to Koinly. There are a couple of ways you can do this:
If you decide to use CSV files, you need to make sure to import your deposits/withdrawals and trades for ALL previous years - not just the current one!
That's all you have to do. Don't forget to tag your airdrops/forks so they show up as Income on your generated cryptocurrency tax forms!